[Equest-users] PSZ Very High Unmet Hours

[Demba Ndiaye]

Adam,

Potential issues with how you model the variable flow...

For sure, there is a problem with supply air temperature for heating. The following is from the Help File:

"Use of HEAT-SET-T for systems SZRH and PSZ is discouraged because it simply overrides the maximum leaving air temperature specified by MAX-SUPPLY-T".

You've set your MAX-SUPPLY-T at 110 F and your HEAT-SET-T at 80 F. You are heating with only 80 F.

_____________
Demba NDIAYE

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Adam Gonthier
Sent: Thursday, July 29, 2010 4:22 PM
To: equest-users at lists.onebuilding.org; bldg-sim at lists.onebuilding.org; Vidya Gowda
Subject: [Bldg-sim] PSZ Very High Unmet Hours

Dear eQuest users,

I am having some difficulty with a project I am working on, and I was hoping I could receive some help or any information on a building a with packaged single zone units with DX cooling and hot water coils for heating, with a VFD to vary the supply flow (there are no VAV boxes in the system, and the supply reacts to overall building pressure rather than specific zonal needs determined by pressure sensors in the ductwork).   There is no reheat in the system either.

It is a LEED for schools project where the simulation of the proposed model shows very high unmet loads for heating and the total energy consumption for space heating is 199 MBTU which is unrealistically low as compared to the baseline model space heating which is 6369 MBTU.  We do not see many unmet hours in the control zone, but since the unit supplies many zones, we are getting very high unmet heating hours in non-control zone spaces.  We are seeing on the order of 4000-5000 hours unmet in many zones.

I have modeled the heating for all zones by specifying the
Heat Source as hot water loop,
The Zone Heat Source is not installed, as the design has no reheat.
Zone entering maximum supply temperature is at 110 degrees.
Hot deck max leaving temp is 80 degrees
Reheat delta T: n/a

Many thanks in advance,
Adam A. Gonthier
Energy Engineer
Horizon Engineering Associates, LLP
347.297.9005
www.horizon-engineering.com<http://www.horizon-engineering.com/>

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